1. Field of the Invention
The present invention relates to a linear-type tape storage magnetic head device which is used for a data backup, for example, on the computer and in which a magnetic tape is used as a medium.
2. Description of the Related Art
Of late, with a trend for a large capacity of the hard disc, the amount of data to be dealt with by a computer system has increased enormously. On that account, there is a growing demand for a data storage system using a magnetic tape as a backup device.
Currently, as the data storage system using the magnetic tape, there are a helical system type using a rotating head and a linear system type using a fixed head. Most formats of the linear system type employ a servo mechanism in accordance with a servo-band system (refer to patent document 1, for example).
FIG. 1 schematically shows a format of the linear system type. The illustration shows a state in which the overall width of a magnetic tape T includes four data bands DB (DB1, DB2, DB3, and DB4) separated by five servo bands SB (SB1, SB2, SB3, SB4, and SB5).
In addition, each of the data bands DB includes data tracks DT constituting a plurality of, for example, 96 pieces of channels as schematically shown in FIG. 2. The data track DT becomes a minimum unit for writing and reading (reproducing) data.
On the other hand, as shown with a broken line in FIG. 1, conventionally a recording and reproducing head HD has a length two times as long as a tape width WT and a magnetic head element portion 101 is provided in the middle portion.
The magnetic head element portion 101 includes, as shown in FIG. 3, a servo signal reproducing magnetic head elements GS (GS1 and GS2) for reading a servo signal written in each of two adjacent servo bands SB with each data band DB in between, and between them, corresponding to a plurality of data tracks DT of the data bands DB, pairs of data recording and reproducing magnetic head elements GD (GD1, GD1, GD2, GD2 . . . and GD8, GD8) arranged respectively maintaining required intervals in the longitudinal direction of the magnetic tape, which serve not only as data recording magnetic head elements for writing a data signal but also as a data reproducing magnetic head element for reading data signals.
In the case of the linear system type, a tape T, as shown by an arrow a in FIG. 1, travels bi-directionally, and in the respective data bands DB, for example, the magnetic head elements GD perform recording and reproducing as moving to and fro twelve times over a predetermined selected set of, for example, eight channels.
The recording and reproducing are performed with respect to the respective channels, that is, data tracks DT by the eight pairs of the data recording and reproducing magnetic head elements GD formed to respectively maintain required intervals in the extending directions of the tracks; and at a time of recording data, with a to-and-fro movement of a tape, one of the pair operates as a recording magnetic head element, and the other operates as a reproducing magnetic head element for monitoring the state of recording in respective pairs.
Then, at a time of reproducing data, reproduction is performed by one of the pair of the recording and reproducing magnetic head elements GD in respective pairs.
Further, in those recording and reproduction of data, tracking servo is performed by a servo signal obtained by the servo signal reproducing magnetic head elements GS1 and GS2.
With respect to the servo signal recorded in the servo band, as shown for example with a recording pattern thereof in FIG. 4, what is called a Chevron structure, that is, a servo system based on a recording format by the servo signal of an angled pattern can be employed.
In addition, when performing, for example, the twelve times to-and-fro recording or reproducing in a target data band DB, at servo bands positioned on the both sides of the data band DB, as shown in FIG. 4, the pair of the servo signal reproducing magnetic head elements GS sequentially moves in the width direction of the servo band SB between lines b1 and b2 that traverse a servo signal in FIG. 4 to obtain servo signals that have different signal intervals corresponding to a position moved, and as a result, the position of the magnetic head element portion 101 can be detected, making it possible to perform position control, that is, the tracking servo. [Patent Document 1] Japanese Published Patent Application 2000-48431 Hereupon, the capacity per tape cartridge of current data storage is approximately 200 MB.
Meanwhile, as mentioned above, since the capacity of the hard disc becomes larger and a high-speed operation has come to be required of the computer, data to be dealt with has increased rapidly. As a result, demand is growing for a large capacity of the tape storage device.
In addition, in order to attain this large capacity, it is necessary to improve linear recoding density as well as track density.
The track density of a tape storage system commercially available is 1k to 2k TPI (Track Per Inch); however, in order to obtain 2 to 4 times larger capacity, the track density of 2k to 5k TPI or more is demanded.
With the servo system currently provided, however, 2k TPI or so is considered to be the limit.
This limit is ascribable mainly to high-speed and precision of the movement due to the large mass of a mechanically movable portion in the servo system.
That is to say, with respect to the magnetic head HD for the linear system, a magnetic gap portion of the magnetic head element needs to be brought in contact with the tape uniformly. Further, the magnetic gap portion needs a fine contact with the tape to smoothly move between the data bands to obtain a uniform sliding condition. Therefore, as described above, the length LH of the magnetic head HD is selected to be two times the tape width WT.
As a result, the magnetic head HD becomes large in terms of size and mass thereof.
In addition, a drive system such as VCM (Voice Coil Motor) or the like is used to track a data track targeted by the magnetic head; however, in order to move a large-size and heavy magnetic head, large power is needed, as mentioned above.
Accordingly, a VCM having a large drive power becomes necessary, with the result that the mechanically movable portion of the servo system including the magnetic head becomes furthermore large. As a result, the drivable range of the VCM is limited to a large extent and a servo range is lowered to several 100 Hz and a TPI to be obtained becomes 2k TPI or so.
On the other hand, expectations are high for reducing back-up time by speeding up the tape traveling time so that data-transfer speed can be improved. The tape speed of the current typical system is more or less 5 m/s, and the speed of 10 m/s to 20 m/s or so is expected in the future. Such speeding up of the tape traveling time requires the servo to accelerate data tracking. That is because the components of high frequency in the frequency of the tape oscillation become larger in proportion to the tape speed.
Accordingly, a tracking system with a favorable response is demanded for obtaining a high density of tracks and for speeding up a transfer time.
The present invention is to provide a linear-type tape storage magnetic head device, in which the track density and the response of the magnetic head are improved by solving the above problems.